1. Field of the Invention
The present invention relates to a mobile station capable of roaming between mobile communication networks, and a wireless communication method.
2. Description of the Related Art
Recently, mobile stations such as mobile phones and Personal Hand phone System (PHS) have been widely used, and a phone call or access to information has become enabled irrespective of time and place. In addition, available regions of mobile stations have expanded, and a phone call or communication has become enabled anywhere at home and visiting using one mobile station.
There is a communication carrier for each area (service area) anywhere at home and visiting, and each communication carrier configures a mobile communication network. Among such mobile communication networks, it is possible to continue a wireless communication with so-called roaming in which a user can receive a same service as that provided by a communication carrier contracted with the user, by switching a communication method or the like. At the time of performing such roaming, a mobile communication network is specified in each area, and a roaming list having information for establishing wireless communication with the mobile communication network is used.
The user can acquire the above-described roaming list through BroadCast/MultiCast Services (BCMSC) for multicasting the same information from a base station to a plurality of mobile stations in an area, or through user's manual operation. A technique has been known in which a roaming list is acquired in the user's own country through e-mail or the like, an updated roaming list is read out without turning the power off, and a mobile communication system is detected, thereby immediately utilizing the update of the roaming list.
If a method of automatically updating a roaming list for all mobile stations through BCMCS or the like as described above is employed, there is a case in which the roaming list cannot be acquired at the updating time since a user turns off the power of a mobile station or the power is kept turned off in stock before selling. BCMCS is a one-way multicast from a communication carrier to mobile stations. Accordingly, there is a case in which the communication carrier side does not grasp an update state of a mobile station, a mobile station does not grasp an update failure and passes over a mobile communication network, and therefore, normal roaming cannot be performed.
Similarly, when update of roaming is performed by the user's own manual operation, the user might forget the update. In addition, for a user who does not recognize a roaming list itself, the update is not performed, and therefore, roaming cannot be performed normally.
To solve such a problem, it might be effective that the frequency of an automatic update by BCMCS is raised to reduce a chance of the update failure. However, update of a roaming list by BCMCS is unnecessarily repeated for a user having a mobile station in which a roaming list is normally updated, thereby resulting in unnecessary consumption of resource or unnecessary increase of the number of accesses.